As a pressure sensor in the related art, there is known a pressure sensor including a piezoelectric element (a piezo element) configured to electrically detect a pressure, a housing configured to accommodate the piezoelectric element and having a tip portion exposed in a combustion chamber, and a pressure transmission member configured to block an internal space in which the piezoelectric element is accommodated from a combustion gas in the combustion chamber and transmit the pressure of the combustion gas in the combustion chamber to the piezoelectric element, wherein a diaphragm configured to close a tip portion of the housing and a plunger disposed to come into contact between the diaphragm and the piezoelectric element are employed as the pressure transmission member (for example, see Patent Literature 1).
In the pressure sensor, the diaphragm is formed to integrally include an outer circumferential flange portion fixed to the tip portion of the housing, a conically inclined portion slightly inclined from the outer circumferential flange portion and having an embossed depth of about 50 μm, and a central flat plate portion in contact with the plunger.
In addition, an annular concave portion is provided in the tip portion of the housing such that a predetermined gap is formed between the diaphragm and a tip-side region of the plunger. Then, a thermal shock error is prevented while preventing a warp due to thermal deformation of the diaphragm.
However, since two members that are referred to as the diaphragm and the plunger are employed as the pressure transmission member, three members including the housing, the diaphragm and the plunger are present as members that is thermally deformed. Therefore, there are more causes of an error due to thermal deformation. In addition, since deformation in the axial direction due to the thermal expansion of the diaphragm and deformation in the axial direction due to the thermal expansion of the housing are not oriented so as to cancel each other out, the detection error in the pressure due to the thermal strain cannot be solved. In addition, since the tip portion of the housing exposed in the combustion chamber has different thicknesses and has an annular concave portion, thermal deformation of the tip portion is not simple. Therefore, the error due to thermal deformation may be promoted. Further, since the number of parts is great, and various kinds of processing are necessary, an increase in costs occurs.
In addition, as another pressure sensor, there is known a pressure sensor including a piezoelectric element (a conversion element) configured to electrically detect a pressure, a housing configured to accommodate the piezoelectric element and having opening to a combustion chamber, and a pressure transmission member configured to block an internal space in which the piezoelectric element is accommodated from a combustion gas in the combustion chamber and transmit a pressure of a combustion gas in the combustion chamber to the piezoelectric element, wherein a diaphragm disposed inside the housing and a rod passing through a central portion of the diaphragm to be exposed in the combustion chamber and in contact with the piezoelectric element are employed as the pressure transmission member (for example, see Patent Literature 2).
In this pressure sensor, the diaphragm is formed to integrally include an outer tubular portion connected to an annular groove formed in an inner wall of the housing, an inner tubular portion connected to an annular groove formed in an outer circumference of the rod, and an annular flat plate portion configured to connect the outer tubular portion to the inner tubular portion. Then, an influence due to thermal deformation of the diaphragm is suppressed.
However, as described above, since the two members that are referred to as the diaphragm and the rod are employed as the pressure transmission member, three members including the housing, the diaphragm and the rod are present as members that generate thermal deformation. Therefore, there are more causes of an error due to thermal deformation. In addition, when the rod expands toward the combustion chamber due to heating, the diaphragm also moves or thermally expands toward the combustion chamber together therewith, and the detection error in the pressure due to the thermal strain cannot be solved. Further, since the number of parts is great, and various kinds of processing are necessary, an increase in costs occurs.